A battery is coupled to a portable battery powered device to provide electrical energy to the device. Many devices use primary batteries which are single cell batteries designed to be discharged one time and then replaced. Another technology widely used is that of rechargeable batteries. These batteries are typically combinations of individual battery cells connected together in series or parallel and placed into a package. The package is fixtured such that it is easily connected and disconnected to the battery powered device, and so that it may be recharged once the electrical energy is used.
One problem inherent to battery powered devices is that the battery has a finite life and as the battery energy nears total depletion, the operation of the battery powered device becomes affected in a negative manner, eventually ceasing to operate. At this point, the battery is typically recharged by removing the battery from the device and placing it in a battery charger. In order to properly charge the battery, the charger must deliver the correct amount of current to the battery over a period of time. If the charger delivers too little current, the battery may not become fully charged. Conversely, if the charger delivers too much current, the battery will become overcharged, overheated, and damaged. Many rechargeable battery packages have some means of sensing the degree of charge of the battery during this operation. This is accomplished by such items as thermistors (for battery temperature measurement) and coding resistors (whose value can identify the proper charge rate and control method). The sensing circuitry can also be used to communicate the condition of the battery to the battery powered device.
U.S. Pat. No. 4,680,527 describes an electrical battery with a current sensing system used to monitor the magnitude of current drawn from the battery during operation. In one embodiment, a total of eight contacts are present on the battery. The contacts and associated interconnection increase the complexity of the battery. Each contact requires a penetration through the housing wall and, thus, is a potential source of moisture intrusion.
In addition, a vent must be provided in the battery housing in order to equalize atmospheric pressure changes to prevent the otherwise waterproof, airtight, sealed housing from "ballooning" and to allow any cell vented gasses (hydrogen, oxygen) from accumulating which could result in an explosion hazard. Vents have two major functions: waterproofing and gas permeability. These vents have been made from a number of materials such as sintered metal, one-way flapper valves, and breathable material such as GORE-TEX.RTM.. Adding such a vent requires an additional hole in the housing and adds an additional cost and manufacturing step to the battery package.
It would also be highly desirable to be able to monitor other functions and parameters of the battery, such as the number of charge/discharge cycles, the capacity rating of the battery, temperature of the battery, the amount of capacity remaining in the battery, the type of battery chemistry, and so forth. In order to communicate each of these parameters to a charger or battery powered device using existing technology, each parameter would require an individual contact in the housing. It may be easily seen that the number of contacts in a housing quickly rises to an unmanageable number if one were to monitor all functions of the battery. If one desires to limit the number of contacts and electrically multiplex on a few lines within the radio and battery, spurious signals could readily result and interfere with the radio operation.
Clearly, an improvement is needed that will provide for a method of monitoring many of these battery parameters while, at the same time, communicating them to a charger or a battery powered device. In addition, a method of venting the battery that does not require an additional vent hole is also desirable.